import java.io.; import java.util.;

public class Solution {

public static void main(String[] args) {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
    Scanner scn = new Scanner(System.in);
    int input = scn.nextInt();

    scn.close();

    AdvancedArithmetic solv = new Calculator(input);

    System.out.println(solv.divisorSum());

}

}

interface AdvancedArithmetic{ int divisorSum(); }

class Calculator implements AdvancedArithmetic{

int arr[];
int n;
Calculator(int n){
    this.n = n;

}

public int divisorSum(){

    System.out.println("I implemented: " + this.getClass().getInterfaces()[0].getSimpleName());

     int sum = 0; 
    for(int i=1; i<=n; i++){
        if( n%i == 0){
           sum += i;
        }
    }
    return sum;
}

}

Here is Day 19: Interfaces problem solution in Python, Java, C++ C and javascript - https://programmingoneonone.com/hackerrank-day-19-interfaces-30-days-of-code-solution.html

Hardly an exercise in Abstractions/Interfaces.

c# conditional operator

public int divisorSum(int n) { int sum=0;

    for(int i=1;i*i<=n;i++)
    {
        var q=Math.DivRem(n,i,out int r);

        if(r==0)
        {
            sum+=i!=q?i+q:i;
        }
    }

    return sum;
}

c#

public int divisorSum(int n) { int sum=0;

    for(int i=1;i*i<=n;i++)
    {
        var q=Math.DivRem(n,i,out int r);

        if(r==0)
        {
            sum+=i;

            if(i!=q)
            {
                sum+=q;
            }
        }
    }

    return sum;
}